The present invention relates to an apparatus and method for qualifying valid data peaks in a read/write channel of a magnetic tape or disk system. More particularly, the present invention relates to a method and apparatus for qualifying valid data peaks occurring in a raw readout signal of the type encountered in a magnetic tape or disk drive data storage device.
In magnetic data storage devices, such as magnetic tape or magnetic disk drives, digital data is stored by selectively magnetizing a magnetic oxide material, or other magnetizable particles, coated on the surface of a suitable media, such as a tape or disk. Stored data is retrieved by creating relative motion between the media and a read head so that the varying magnetic flux associated with the stored data generates an electrical signal in the read head, which electical signal varies as a function of the intensity of the change in magnetic flux, and which change in magnetic flux, in turn, varies as a function of the stored data. This electrical signal generated within the read head is hereafter referred to as a "raw readout signal," and this term applies for purposes of this application whether the signal has been amplified or not, filtered or not, or otherwise buffered and processed prior to being applied to the data peak qualification circuitry of the present invention.
The amplitude of the raw readout signal is highest at a point coincident with the greatest change in magnetic flux. Such points of greatest flux change are typically used to indicate data transitions of the data being stored. Hence, in order to accurately recover or retrieve the stored data, it is necessary to detect this highest point of the raw readout signal, referred to hereafter as a signal or data peak. Because flux changes may occur in one of two directions, the signal peaks to be detected may be either positive or negative peaks.
Unfortunately, irregularities may exist in the magnetic recording media, and electrical noise or other sources of electrical irregularities may occur within the read/write channel causing more than one data peak to be present within the raw readout signal for a given data transition that is desired to be stored on the magnetic media. Therefore, for the data to be accurately retrieved from the storage media, some sort of method and apparatus is needed to qualify which of a plurality of data peaks are to be interpreted as a valid data peak. The present invention is directed to such a method and apparatus for qualifying valid data peaks.
It is known in the art to use threshold detectors to disqualify data peaks whose amplitude does not exceed a prescribed level. However, false data peaks may readily exceed a prescribed threshold, and therefore threshold detection is not, by itself, an adequate means for qualifying data peaks.
It is also known in the art to detect signal slope, in combination with signal amplitude change, in order to select or qualify valid data peaks. See, U.S. Pat. No. 3,631,263. While this approach represents a significant improvement over mere threshold detection, the circuitry required to realize such a scheme is quite complex and expensive to fabricate and maintain. Moreover, the signal slope, or shape of the peak, is not always an accurate indicator of which data peaks are valid and which are not.